Background: Renal osteodystrophy (ROD) is a term used to represent the spectrum of metabolic bone disease is present in almost all patients with uremia. Although bone biopsy/bone histomorphometry remains the gold standard for the diagnosis for the subtype of ROD, it is rarely employed clinically because it is an invasive procedure. Consequently serum levels of parathyroid hormone and alkaline phosphatase are used as non-invasive markers to diagnose and treat ROD. These markers are relatively nonspecific. The bone markers used in the general population to estimate bone turnover have not been successfully applied to uremic patients because of decreased urinary excretion and resulting accumulation in the plasma. Patients undergoing continuous ambulatory peritoneal dialysis are likely to have nearly constant serum level of collagen degradation products, while the daily burden of these molecules is removed by peritoneal dialysis. Therefore, it should be possible to measure these molecules in the peritoneal effluent as a measure of collagen breakdown. Specific Aims: To assess in end-stage renal disease (ESRD) patients receiving chronic peritoneal dialysis, (1) the validity of non-invasive markers of bone turnover including 24 hr generation of N-terminal telopeptide of collagen (G-NTx), deoxypyridinoline (G-DPD) normalized for creatinine (G-Cr) in the peritoneal dialysis effluent (G-NTx: G-Cr and G-DPD:G-Cr), intact PTH, 1-84 PTH, bone-specific alkaline phosphatase (BSAP), osteocalcin (OC) and tartrate resistant acid phosphatase (TRAP), DPD and NTx in comparison to bone turnover measured by bone histomorphometry; (2) the peritoneal clearance of NTx as a marker of "a middle molecule" and compare with clearance of small molecules i.e. urea and creatinine; and (3) to obtain preliminary data for evaluation of racial differences in bone turnover for future studies. Outcome: A better assessment of noninvasive markers to determine ROD will enhance treatment strategies without the need for invasive procedures. The utility of peritoneal clearance of NTx as a simple determinant of dialysis adequacy may change our present paradigms for assessing the efficacy of ESRD treatment. Finally, data on bone turnover in peritoneal dialysis patients from the three different racial groups (African American vs. Caucasian vs. Hispanic) may provide preliminary evidence for racial differences that could be used to design future prospective studies to evaluate racial differences in the prevention/treatment of ROD.